According to Slashfilm, that’s Decepticon The Fallen who appears in its Cybertronian form. Some say that he's responsible for the Decepticons split from Cybertron... looks a bit like Sauron (LOL), but most Transformers fans would agree that this is a life-like version of the Decepticon logo!!
Message from Michael Bay:
Okay it’s time to turn up the heat on Transformers - Revenge of the Fallen. We’ve waited low in the weeds letting all the summer movies get their stuff out. We’ve seen the great year end movies, and watched the upcoming clips of the upcoming summer fare. We’ve seen certain movies coming out even try to duplicate Transformer size robots in their ads. Please, come on. Well, I promise you we will rock your world with Transformers 2. The fans wanted ROBOTS KICKING ASS - well we got it. Today we are releasing the teaser poster and soon the onslaught will continue with a steady drum beat until June 26th.
Edit:
I've found out that my white template contrasted greatly with the poster, making it appear darker (due to an optical illusion). Here's the optimised version - just some tweaking with brightness & contrast:
